The invention relates to a method of manufacturing a long watertight cable or cable joint comprising a number of conductors situated within an outer sheath, in which a liquid or semisolid sealing mixture comprising a vulcanizable silicone rubber and a diluent is provided in the space between the conductors mutually and between the conductors and the outer sheath, which mixture, after vulcanization of the silicone rubber, provides a watertight seal.
Such a method directed to the manufacture of long watertight cables is known from published Netherlands Pat. application No. 7,408,740 in the name of Applicants.
According to the known method, a silicone rubber is used which is vulcanizable under the influence of moisture and which may contain a silicone oil or a rapidly evaporating solvent as a diluent.
It has been found that a diluent which is permanently present in the water tight seal formed after vulcanization of the silicone rubber promotes the desired properties of the material, such as elasticity and moisture tightness.
The known permanent diluent, silicone oil, gives good satisfaction but for practical application has the important disadvantage of being very expensive and in addition causing skin irritation so that special protection measures have to be taken by the operating personnel.
Despite intensive efforts, the art has until now failed to provide diluents which in combination with silicone rubber show the same favorable characteristics as regards adhesion, elasticity and moisture tightness as the known combination of silicone rubber and silicone oil, but which do not have the above-mentioned disadvantages. The usual solvents for silicone resins, or in other words for organopolysiloxanes, as shown, for example, in German Auslegeschrift 1,795,198, failed to meet these requirements.
It is an object of this invention therefore, to provide a diluent for vulcanizable silicone rubber which is less expensive than the silicone oils and is relatively non-irritating to the skin while with the silicon rubber showing the same favorable characteristics as regards adhesion, elasticicity and moisture tightness. This and other advantages of the invention will be apparent from the description that follows: